The depth of field (DOF) of an image is a range of scene depths at which objects in a scene appear to be in-focus in an image of the scene. In most applications of imaging, from consumer digital photography to optical microscopy, it is desirable to control the DOF of an image being captured. Capturing images with a very large DOF is particularly appealing given that, as the depth of field increases, more of the scene can be shown in focus. However, some conventional techniques for increasing depth of field, such as decreasing the aperture of a camera, have limitations. For example, with a smaller aperture, less light is received at an image sensor (or film), and this can require longer exposures which can decrease the signal to noise ratio and cause blurring due to camera shake and/or objects in the scene moving. Furthermore, as pixel size decreases (and/or as sensor resolution increases), the DOF of an image decreases because any defocus blur present in the image occupies a greater number of pixels. At the same time, each pixel receives less light which can cause the signal to noise ratio to fall as well. This trade-off between the DOF and the signal to noise ratio is one of the fundamental, long-standing limitations in imaging.
Two other limitations on DOFs in images are that: (1) many cameras can only capture a single limited DOF that corresponds to a single range in the scene; and (2) the DOF in an image is typically fixed and cannot be altered by a user after capturing an image. Because of this single, fixed DOF, only objects within the DOF are captured in-focus and objects in the scene outside of the DOF are blurred to some extent. This can inhibit, for example, a user from capturing an image where an object that is close to the camera (e.g., inches to a few feet away) and objects that are far from the camera (e.g., several feet to dozens of feet away) are both in-focus, forcing the user to choose which object to capture in an in-focus state.
Therefore, there is a need for mechanisms that can provide interactive refocusing in images over multiple depths of field and can provide images with an extended depth of field.